This invention relates to sewing machines; more particularly, to an auxiliary feed stitch regulating mechanism for a sewing machine having a differential feed capability.
There is a class of industrial sewing machines having a differential feed capability wherein the feeding rate of the main feed dog is set by one stitch length regulator and the feeding rate of an auxiliary feeding dog is set by a second stitch regulator which, generally, increases the feed obtainable from the sewing machine feed rock shaft. In most cases, the auxiliary feed dog is carried by a rod slidable in bosses extending from the main feed dog carrier so as to maintain both feed dogs in rising and falling synchronism. The auxiliary feed stitch regulator thus drives the rod carrying the auxiliary feed dog relative to the main feed dog carrier in order to, for example, create a pucker in the work material of variable degrees for decorative or utilitarian purposes. In many industrial sewing machines, the feed ratio between the auxiliary feed dog and the main feed dog is generally adjusted to a position and maintained there. However, in certain cases, it is desirable to provide a way for an operator to vary the ratio between the auxiliary feed and the main feed in order that a greater variety of stitching possibilities may be accommodated. In these types of machines, the auxiliary feed stitch regulator mechanism may be varied while the sewing machine is operating by means of a treadle control which adjusts the amount of motion derived from the feed rock shaft. One of the problems encountered with this type of device is a feedback from the rock shaft to the foot of the sewing machine operator by the treadle which, at best, is annoying, generates operator fatigue and may actually affect the appearance of the work material in having a non-uniform gather.
What is required is some means of isolating, insofar as possible, the vibration of the rock shaft from the operator of the sewing machine so as to avoid the feedback to the operator of the motion of the rock shaft and the variability in the product that may result from an operator's response to this feedback.